(i) Technical Field
The present invention relates to an optical semiconductor device and a method of manufacturing the optical semiconductor device.
(ii) Related Art
Japanese Patent Application Publication No. 2008-244264 discloses a semiconductor laser in which a mesa stripe including an active layer is buried with a high resistivity semiconductor layer made of InP including Fe. The semiconductor laser may be manufactured through a process of burying the mesa stripe with the high resistivity semiconductor layer after forming the mesa stripe. In the semiconductor laser, an element capacity is reduced, and frequency band of a direct modulation gets wider.
However, in the semiconductor laser, Fermi level of the high resistivity semiconductor layer is positioned at intermediate of a band gap. Therefore, an electron tends to leak from the active layer to the high resistivity semiconductor layer when the active layer is buried with the high resistivity semiconductor layer. In this case, leak current bypassing the active layer may be increased when providing high current or operating at high temperature. In this case, optical outputting may be restrained.